Prismatic reflectors

ABSTRACT

Prismatic reflectors for use with clear light sources in which spiral flutes are disposed over at least a lower portion of the interior surface. The flutes run in two directions to form a plurality of diamond shaped areas for spreading light incident thereon in both horizontal and vertical directions. Double faced prisms are provided over a top portion of the interior surface of the reflector for the purpose of causing a predetermined amount of light to be reflected to the nadir of the reflector.

UnitedStates Patent [191 Welty [111 3,809,881 [451 May 7,1974

[ PRISMATIC REFLECTORS [75] Inventor: Dale E. Welty, Newark, Ohio [73] Assignee: Holophane Company, Inc., New

York, NY.

[22] Filed: July 17, 1972 {21] Appl. No.: 272,312

[52] US. Cl. 240/106 R, 240/25, 240/103 R [51] Int. Cl. F2lv 7/00 [58] Field of Search 240/103 R, 106 R, 25

[56] References Cited UNITED STATES PATENTS 10/1966 Franck 240/25 6/1930 Cole 240/106 R Hamel 2,499,580 3/1950 240/106 R 3,678,458 7/1972 Ljungku1letal.... 240/106 R 1,948,555 2/1934 Wood 240/106 R 3,562,513 2/1971 Jaffe et al. 240/106 R 3,270,197 8/1966 Fouke 240/106 R 3,062,953 11/1962 Clark et al. 240/106 R 2,201,094 5/1940 Kassel 240/106 R Primary Examiner.loseph F. Peters, Jr. Attorney, Agent, or Firm-R. M. Krone; S. C. Shear [5 7] ABSTRACT Prismatic reflectors for use with clear light sources in which spiral flutes are disposed over at least a lower portion of the interior surface. The flutes run in two directions to form a plurality of diamond shaped areas for spreading light incident thereon in both horizontal and vertical directions. Double faced prisms are provided over a top portion of the interior surface of the reflector for the purpose of causing a predetermined amount of light to be reflected to the nadir of the reflector.

12 Claims, 6 Drawing Figures m nnow 7:914 3.809.881

sumaorz Fig. 3

SINGLE SOURCE VARIOUS POSITION THREE SOURCES SINGLE POSITION CANDLE POWER CANDLE POWER 1 PRISMATIC REFLECTORS BACKGROUND OF THE INVENTION Prismatic reflectors are well-known and have found particular use in various types of industrial lighting applications. An example of a known prismatic reflector is found in US. Pat. No. 2,710,340.

It has only been recently that clear lamps, such as clear metal halide and clear high pressure sodium, have been produced in which the arcs of such lamps produce light with acceptable color characteristics. Previously it was necessary to coat the interior surface of the lamps to obtain such acceptable color characteristics. Prismatic reflectors, in turn, were designed to produce uniform distributions of light from coated lamps.

It has been found that when attempts to substitute a clear lamp for a coated lamp are made in a known prismatic reflector, problems are encountered. The reason for this is that reflectors designed for coated lamps receive light from essentially the whole of the fairly large lamp, whereas light from clear lamps is produced only by a thin elongated arc. The particular problems encountered are (l) irregularities in candlepower distribution over normal angular ranges and (2) the occurrence of excessive or deficient amounts of light at the nadir of the light distribution of the reflector.

The first problem, it has been found, is caused as a result of the candlepower distribution curves of a reflector being highly sensitive to unavoidable discontinuities in the design of the reflector and from imperfections in the mold equipment which produces the reflector. Even though such imperfections are minute and would not significantly affect candlepower distributions when coated lamps are employed in a reflector, intolerable irregularities in the distribution are produced when clear lamps are used. The second problem of light starvation" or buildup" at the nadir is caused as a result of the reflector being highly sensitive to small variations in the position ofa clear lamp away from a standard position. For each lamp, there is a standard" position at which an optimum candlepower distribution is produced from the top portion of the reflector and, with coated lamps, small variations from the standard position will not significantly change the amount of light at nadir. Again, this is due to the fact that with coated lamps, essentially the whole lamp produces light and hence, a variation of say one-half inch from a standard position will not have a significant effect.

As stated above, the buildup or starvation of light at nadir occurs as a result of reflections from the top portion of the reflector. When viewing the reflector from higher angles (with respect to the nadir) a spot or line of light is viewed on the far side of the reflector. As the angle of viewing the reflector is reduced, the line or spot of light moves up the side of the reflector until the angle of viewing is along the nadir at which point the light appears as a ring completely around the top of the reflector. Depending on the position of the light source with respect to the reflector, the source may or may not be flashed across the top of the reflector producing a high candlepower level or low candlepower level, respectively at nadir.

SUMMARY A prismatic reflector for use with clear light sources has interior and exterior surfaces and upper and lower edges, spiral flutes on said interior surface for spreading light incident thereon to thereby obtain a regular distribution of reflected light, said spiral flutes extending over at least a portion of said internal surface.

As noted above, slight variations in the positioning of a coated light source do not result in significant changes of the angular distribution of candlepower of the reflector. Thus, it is an object of the present invention to provide a reflector that functions with a clear light source as if a coated light source were employed. As coated light sources have a greater vertical length and horizontal width, the reflector of the present invention is designed to achieve both a horizontal and vertical diffusion of light within the light pattern without actually changing the basic light distribution pattern of the reflector.

The desired spreading is achieved by providing two sets of flutes, each set extending upwardly from the bottom edge of the reflector in a spiral fashion. The sets of flutes are arranged at angles to one another and cross to form a plurality of small diamonds on the interior surface, each diamond having a lateral (horizontal) and vertical component of spread. In this way a degree of spread is achieved without spreading light so much as to go beyond the angle of acceptance of the reflecting prisms on the exterior surface of the reflector.

The spiral flutes of the reflector of the present invention may extend to the upper edge of the reflector. However, it is preferred to desensitize the top portion of the interior surface of the reflector by providing a plurality of horizontally arranged, double faced prisms. These prisms transmit light, as will be discussed subsequently in detail, in such a way that a predetermined amount of light is reflected to nadir. In this manner the problem of light starvation or light buildup at nadir as previously discussed is avoided.

BRIEF DESCRIPTION OF THE DRAWING Prismatic reflectors embodying the present invention will now be described, by way of example, with reference to the accompanying drawing, in which:

FIG. 1 shows a partial elevation view of a prismatic reflector of the present invention with spiral flutes and prisms on the internal surface thereof,

FIG. 2 shows an enlarged view of an upper portion of the reflector of FIG. 1,

FIG. 2A shows the same enlarged view as shown in FIG. 2, except that the incident light rays emanate from the bottom of the light source.

FIG. 3 shows a partial elevational view of another embodiment of the present invention,

FIG. 4 shows typical candlepower distributions of a prior art prismatic reflector when employed with a single clear light source at various mounting positions, and

FIG. 5 shows candlepower distributions of the prismatic reflector of the present invention when employed with three typical clear light sources.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1 of the drawing, there is shown a portion of a prismatic reflector 10 which is circular in horizontal cross section. Reflecting prisms 11 are provided on the external surface of reflector 10 as spiral flutes 12 and 14 extending upwardly from the lower edge of reflector 10 are provided on the interior surface of reflector l0. Flutes 12 are at an angle to flutes 14 and thereby form a plurality of diamonds on the interior surface of reflector 10.

A clear light source 27 having an are 21 is disposed in the center of, and toward the top of, reflector 10. Parallel rows of horizontal prisms 33, each prism having a double face 13 and an inactive face 29 are provided on the upper portion of the interior surface of reflector l0. Rays of light 22 and 23 from the top and bottom of are 21 will be described subsequently with respect to FIG. 2.

As noted above, light from are 21 incident on the diamonds formed by flutes l2 and 14 is spread in both horizontal and vertical directions. This spreading or diffusion has the effect of causing the are 21 to resemble a coated light source when light is transmitted through the interior surface of reflector 10 to be reflected. As a result, smooth distribution curves l8, l9 and 20 of FIG. are obtained for three different clear light sources and the irregularities occurring in distribution curves I5, 16 and 17 for a single source at various positions (of FIG. 4) are avoided.

Referring now to FIG. 2, there is shown an enlarged elevational view of the upper portion of reflector 10. Double faced prisms 13, each have individual faces 24 and 25 and an inactive face 29 are provided on the interior surface of reflector as previously discussed. Light rays 22 and 23 are transmitted through faces 24 and 25 and are reflected from reflecting prisms 11, which appear linear in the elevational view shown.

Faces 24 and 25 of prisms 13 act to supply a predetermined, desired amount of light at nadir of reflector l0 and thereby avoid the problem of light starvation or buildup. A ray of light 22 from the top of arc 21 is refracted upwardly by face 24, reflected from prism 11 and refracted downwardly toward nadir by face 24' of an adjacent prism 13'. In practice, ray 22 will leave the interior surface of reflector 10 at a small angle, say 0 to 5 and thereby provide a desired amount of light at nadir. The total amount of light at nadir then will be determined by the number of similar rays 22 reflected from other horizontal prisms 33 and the relative areas of faces 24 and 25. For example, if the area, or side length, of prism face 24 is substantially greater than the area or side length of prism face 25, a greater amount of. light will be reflected toward nadir. In this manner, the total amount of light at nadir may be predetermined by the number of prisms 33 and by the design of faces 24 and 25 and corresponding faces of other horizontal prisms 33.

A ray of light 22' incident on lower face 25 of prism 13 is reflected and emitted from face 25 of prism 13 as ray 22' at an angle substantially away from nadir although well within a desired angular range.

Referring now to FIG. 2A, rays 23 and 23' from the bottom of are 21 are incident upon faces 24 and 25 of prism 13, respectively. Rays 23 and 23' are reflected by prisms l 1 and are emitted by faces 24' and 25' of prism 13', respectively. Also, rays 23 and 23' are directed substantially away from nadir although well within a desired angular range. Furthermore, prisms l3 and 13', as well as all other prisms, provide a more uniform distribution of light as a result of spreading arc 21. In this context, .the term spreading refers to the extent to which the length of are 21 is increased by reflection. If, for example, the angle between the reflected rays were equal to the angle of rays 22 and 23 as shown in FIG. 1, there would be no spreading of are 21. However, by providing double faced prisms 13, 13, etc., it will be seen that the angle between emitted rays 23' and 22, as

shown in FIGwZA, is greater than the angle between rays 22 and 23 of FIG. 1.-Thus, as reflected, the length of are 21 is greater than the actual length as shown in FIG. and a more uniform distribution of reflected light is hereby obtained.

As a result of the present invention, the problems of starvation or buildup of light at nadir (0) which exist in prior art reflectors employing clear light sources and as shown in FIG. 4 are avoided. Thus, slight deviations of light source 27 from a standard position can be made and still maintain a rather constant amount of light at nadir thereby avoiding the problem of light starvation or buildup.

In FIG. 3, a reflector 10 is shown in which spiral flutes 12 and 14 are provided on the interior surface thereof and extend from the lower edge to the upper edge of the reflector. While no prisms are provided on the top portion of the interior surface as shown in FIG. 1, acceptably uniform candlepower distributions may be obtained when clear lamps are employed.

I claim:

1. A prismatic reflector for use with clear light sources, said reflector having interior and exterior surfaces and upper and lower edges, spiral flutes on said interior surface for spreading light incident thereon to thereby obtain a regular distribution of reflected light, said spiral flutes extending over at least a portion of said interior surface said reflector further including prismatic elements disposed on an upper portion of said interior surface, said prismatic elements having two active face prisms disposed substantially annularly, said prisms refracting light incident thereon to provide a predetermined amount of reflected light at the nadir of said reflector.

2. The reflector of claim 1 in which said spiral flutes are comprised of first and second sets of flutes, said first set beingat an angle to said second set whereby a plurality of diamonds is formed over a portion of said interior surface of said reflector.

3. The reflector of claim 2 in which said first and second sets of spiral flutes extend upwardly from said lower edge substantially over a lower portion of said interior surface.

4. The reflector of claim 1 in which said prisms have an upper and lower face, said upper face being disposed at a smaller angle with respect to the nadir than said lower face such that incident light transmitted by said lower face is reflected substantially away from said nadir.

5. The reflector of claim 4 in which the reflector is circular in horizontal cross section and in which the arc of a lamp is vertically disposed in a line extending perpendicularly through the center of said circular cross section.

6. The reflector of claim 5 in which light from the top of said are incident upon said upper face of one of said double faced prisms is reflected toward to said nadir while light from the bottom of said are incident on said lower face is reflected substantially away from said nadir.

7. A prismatic reflector for use with clear light sources, said reflector having interior and exterior surfaces and upper and lower edges, means for reflecting light from said source, said means being disposed on an upper portion of said exterior surface, and prismatic elements disposed on an upper portion of said interior surface, said prismatic elements having two active face prisms disposed substantially annularly, said prisms refracting light incident thereon to provide at nadir of said reflector a predetermined amount of reflected light from said reflecting means.

8. The reflector of claim 7 in which said prisms have an upper and lower face, said upper face being disposed at a smaller angle with respect to the nadir than said lower face such that incident light transmitted by said lower face is reflected substantially away from said nadir.

9. The reflector of claim 8 in which the reflector is circular in horizontal cross section and in which the arc of a lamp is vertically disposed in a line extending perpendicularly through the center of said circular cross section.

10. The reflector of claim 9 in which light from the top of said are incident upon said upper face of one of said double faced prisms is reflected toward said nadir while light from the bottom of said are incident on said lower face is reflected substantially away from said nadir.

11. A prismatic reflector for use with clear light sources, said reflector having interior and exterior surfaces and upper and lower edges, said lower edge being located below the lowermost point of the light source and defining the lowermost extent of said reflector, means for reflecting light from said source, said means being disposed on said exterior surface, first and sec- 0nd sets of spiral flutes formed over substantially the entire interior surface of said reflector and extending from said lower edge to said upper edge for spreading light incident thereon to therey obtain a regular distribution of light reflected from said reflecting means, said first set of flutes being at an angle to said second set of flutes whereby a plurality of diamonds is formed over said interior surface for horizontally and vertically diffusing said reflected light.

12. The reflector of claim 11 in which the reflector is circular in horizontal cross section and in which the arc of a lamp is vertically disposed within said reflector in a line extending perpendicularly through the center of said circular cross section. 

1. A prismatic reflector for use with clear light sources, said reflector having interior and exterior surfaces and upper and lower edges, spiral flutes on said interior surface for spreading light incident thereon to thereby obtain a regular distribution of reflected light, said spiral flutes extending over at least a portion of said interior surface said reflector further including prismatic elements disposed on an upper portion of said interior surface, said prismatic elements having two active face prisms disposed substantially annularly, said prisms refracting light incident thereon to provide a predetermined amount of reflected light at the nadir of said reflector.
 2. The reflector of claim 1 in which said spiral flutes are comprised of first and second sets of flutes, said first set being at an angle to said second set whereby a plurality of diamonds is formed over a portion of said interior surface of said reflector.
 3. The reflector of claim 2 in which said first and second sets of spiral flutes extend upwardly from said lower edge substantially over a lower portion of said interior surface.
 4. The reflector of claim 1 in which said prisms have an upper and lower face, said upper face being disposed at a smaller angle with respect to the nadir than said lower face such that incident light transmitted by said lower face is reflected substantially away from said nadir.
 5. The reflector of claim 4 in which the reflector is circular in horizontal cross section and in which the arc of a lamp is vertically disposed in a line extending perpendicularly through the center of said circular cross section.
 6. The reflector of claim 5 in which light from the top of said arc incident upon said upper face of one of said double faced prisms is reflected toward to said nadir while light from the bottom of said arc incident on said lower face is reflected substantially away from said nadir.
 7. A prismatic reflector for use with clear light sources, said reflector having interior and exterior surfaces and upper and lower edges, means for reflecting light from said source, said means being disposed on an upper portion of said exterior surface, and prismatic elements disposed on an upper portion of said interior surface, said prismatic elements having two active face prisms disposed substantially annularly, said prisms refracting light incident thereon to provide at nadir of said reflector a predetermined amount of reflected light from said reflecting means.
 8. The reflector of claim 7 in which said prisms have an upper and lower face, said upper face being disposed at a smaller angle with respect to the nadir than said lower face such that incident light transmitted by said lower face is reflected substantially away from said nadir.
 9. The reflector of claim 8 in which the reflector is circular in horizontal cross section and in which the arc of a lamp is vertically disposed in a line extending perpendicularly through the center of said circular cross section.
 10. The reflector of claim 9 in which light from the top of said arc incident upon said Upper face of one of said double faced prisms is reflected toward said nadir while light from the bottom of said arc incident on said lower face is reflected substantially away from said nadir.
 11. A prismatic reflector for use with clear light sources, said reflector having interior and exterior surfaces and upper and lower edges, said lower edge being located below the lowermost point of the light source and defining the lowermost extent of said reflector, means for reflecting light from said source, said means being disposed on said exterior surface, first and second sets of spiral flutes formed over substantially the entire interior surface of said reflector and extending from said lower edge to said upper edge for spreading light incident thereon to therey obtain a regular distribution of light reflected from said reflecting means, said first set of flutes being at an angle to said second set of flutes whereby a plurality of diamonds is formed over said interior surface for horizontally and vertically diffusing said reflected light.
 12. The reflector of claim 11 in which the reflector is circular in horizontal cross section and in which the arc of a lamp is vertically disposed within said reflector in a line extending perpendicularly through the center of said circular cross section. 